HARDWICKE'S SCIENCE-GOSSIP. 



133 



the young, which are six-legged, are frequently met 

 with. Snakes are infested by a species of Ixodes 

 called by Mr. Murray Ophiodes ; but little seems to 

 be known regarding the differences of the various 

 species. 



Before considering the Acari, we may notice two 

 large and important divisions of the Ixodes, viz. : — 



I. Trombidiidse, or harvest-mites, which are sub- 

 divided into several families. It may suffice to 

 mention the Tctranychiis autumnalis, or harvest-bug, 



Fig. 88. — Flea of Birds, enlarged. 



the beetle, and also on the humble bee. Another 

 weli-known species is the Dermanyssus avium, which 

 is common about the cages of canaries and other cage- 

 birds ; species very closely allied frequent swallows'- 

 nests and also poultry-houses. 



The Acari proper are divided into a large number 

 of sub-genera, and are a subject of very great interest ; 

 but space will not permit my doing more than 

 mentioning a few of the many interesting species 

 which are found leading a parasitic life. 



1. Hypoderidoe, found living between the skin and 

 muscle of some birds, such as the pigeon. They are 

 oblong, oval, and almost transparent. 



2. Dermaleichidx. — This sub-genus contains by far 

 the largest number of species, almost every bird 



Fig. 8q. — Flea of Squirrel [Pulex sciurorum), male, enlarged. 



Fig. 90. — Listophorus of 

 Hare. X 100. 



Fig. 91. — Dermaleichus of 

 Chaffinch. X 100. 



Fig. 92. — Hypopus of Fly. Fig. 93. — Harvest-Bug [Tetra- 

 X 220. nychus autumnalis). X 100. 



which is of a brick-red colour, and so minute as 

 scarcely to be visible to the naked eye. They live 

 among bushes and grass, and fix themselves to 

 passers-by, causing much uneasiness and pain. 

 Another well-known species of the Trombidiidre is 

 the Scirus insectorum, which is the small red parasite 

 frequently found on the harvest spider and other 

 insects. 



2. Gamasidre. — This is a large family, the greater 

 number of which are parasitic. Perhaps the best- 

 known species, and one showing the principal features 

 of the family, is Gamasus colcoptratorum, found on 



having one peculiar to itself, and several being 

 infested by two or three distinct varieties ; in the 

 latter case we find that each variety, as a rule, fre- 

 quents a different part of the body, the primary 

 feathers of the wing being a favourite resort, where, 

 from their small size, these parasites look like fine 

 dust. Figure 91 shows a typical example. In some 

 species, such as one of the varieties found on the 

 sparrow, the third pair of legs are very much enlarged 

 in the males, but are of the normal size in the females. 

 The body is covered by a chitinous skin, which is 

 delicately striated. 



